1. Field of the Invention
The present invention relates to toner and developer that are used in the development by printers, electro-photographic apparatus and the like, and methods for manufacturing toner and developer.
2. Description of the Related Art
In electro-photographic apparatus or electrostatic recording devices, a two-component developer is used for developing an electrostatic latent image that is formed on a photo-conductive drum or an electrostatic image carrier made of a dielectric to a visible image. This two-component developer comprises toner and carrier. Generally, this toner is manufactured as colored fine particles in such a manner that coloring agents and other additives are mixed in a fused state in thermoplastic resin, and after uniformly dispersed, a solidified product is finely pulverized and classified to a desired particle size. Further, in recent years the development of images from monochrome color to full colors has been largely advanced in electro-photographic apparatuses or electrostatic recording devices and in general, all colors are reproduced using three color toners in yellow, cyan and magenta colors that are three primary colors.
In general, toner in a two-component developer is charged to a fixed amount and polarity by friction with carrier and adsorbed to an electrostatic latent image using the electrostatic attraction to develop the image. Therefore, the friction charge characteristic of toner that is determined by the relation with carrier is required to be satisfactory.
Further, for toners used in the full color development, an excellent transferring characteristic is demanded because a multiple-colored image is reproduced by superposing respective color toner. The transferring characteristic is largely concerned with a charge amount of toner. If the charge amount of toners is too high, adhesion power of toner to a photo-conductive drum becomes strong and transferring efficiency is lowered. Further, transferring efficiency to a paper is also lowered even when the charge amount distribution of toner is broad. On the contrary, if the charge amount of toner is too low, the toner may scatter and contaminate the inside of an apparatus or a fog may be produced on the non-image portion of a paper when an image is transferred or toner may be mixed in another image portion and an image becomes unclear and turbid.
In particular, such color toners as yellow, cyan and magenta colors do not contain such conductive materials as magnetic powder and carbon black as in a black toner. Accordingly, color toner has no portion to leak frictional charge and the charge amount of toner is not stabilized and tends to become large. Further, the charge amount is susceptible to the influence of temperature and humidity and such troubles are caused as excessive charge amount under a low humidity and insufficient charge amount under a high humidity and it was difficult to maintain the charge amount stably under all environments.
In regard to the above-mentioned problems, fine particles that are called external additives are so far added to the toner particle surfaces as a means to give charge stability, fluidity, durable stability, etc. to toner of two-component developer. In the case of color toner, it is known that such metallic oxide fine particles as titanium oxide that do not affect the hue of toner are used as external additives as conductive material like carbon black in black toner.
As examples of titanium oxide used as an external additive, Japanese Patent Application Laid-Open No. 48-47345 disclosed the use of it as an abrasive, Japanese Patent Application Laid-Open Nos. 52-19535 and 56-128956 disclosed as a fluidity agent and Japanese Patent Application Laid-Open Nos. 58-185405 and 58-216252 disclosed as a surface processed titanium oxide to give positive charging property, Japanese Patent Application Laid-Open Nos. 58-1157 and 60-136755 disclosed charge control agent to suppress charge amount of silica when jointly used with hydrophobic silica. Further, Japanese Patent Application Laid-Open Nos. 60-112052 and 5-188633 disclosed anatase titanium oxide, Japanese Patent Application No. 59-52255 disclosed alklkyl trialkoxysilane processed titanium oxide and Japanese Patent Application Laid-Open No. 7-244397 disclosed rutile titanium oxide, respectively.
However, when titanium oxide was applied to color toners as an external additive, charge stability, fluidity, durable stability, etc. were not always satisfactory. For instance, when rutile titanium oxide was used, surface activity was small and hydrophobic process was not always sufficiently applied. Further, the hydrophobic degree of titanium oxide could be increased by using much processing agent or using high viscosity processing agent, etc. However, different kinds of particles were adhered to each other so that combined particles were produced or the hydrophobic process was not uniform at the stage of the hydrophobic processing and thus, the hydrophobic process was not sufficient. Therefore, toners were inferior in fluidity and there was such a problem that a toner clamp tends to occur so as not to satisfactorily supply toner from cartridge to a developing device.
Therefore, when rutile titanium oxide was jointly used with silica in order to make up for fluidity, a new problem to impair the charging characteristic of toner was caused. Further, Japanese Patent Application Laid-Open No. 7-244397 disclosed a method to make the union of different kinds of particles difficult by making rutile titanium oxide hydrophobic uniformly in a short time by processing with organic matter after the surface processing of rutile titanium oxide with inorganic oxide. However, the hydrophobic degree is restricted up to 80% and it is difficult to obtain the hydrophobic degree above it and an improvement was required.
On the other hand, on anatase titanium oxide, there were such problems that its inherent volume resistance is low, charge leakage from toner at high humidity is fast and change is not stable, etc.
An object of the present invention is to provide toner, developer and methods for manufacturing toner and developer, capable of obtaining stabilized charging characteristic irrespective of environmental conditions such as temperature, humidity and the like, and obtaining clear and good full color images without impairing color reproducibility, transparency, fluidity of toner and causing fogs and scattering of toner to surroundings.
According to the present invention, there is provided toner comprising toner particles containing binder resin and coloring agents; rutile/anatase mixed crystal titanium oxide externally added to the toner particles and hydrophobic processed; and hydrophobic silica externally added to the toner particles.
Further, according to the present invention, there is provided developer comprising toner particles containing binder resin and coloring agents; rutile/anatase mixed crystal titanium oxide externally added to the toner particles and hydrophobic processed; hydrophobic silica externally added to the toner particles; and silicon resin coated carrier.
Further, according to the present invention, there is provided a method for manufacturing toner comprising the steps of preparing toner particles; and externally adding hydrophobic processed rutile/anatase mixed crystal titanium oxide and hydrophobic silica to the toner particles simultaneously.
According to the present invention, there is provided a method for manufacturing developer comprising the steps of manufacturing toners by externally adding hydrophobic processed rutile/anatase mixed crystal titanium oxide and hydrophobic silica simultaneously to toner particles; and mixing the toner and silicon resin coated carrier.